Field
Embodiments relate to associating user equipment (UE) with multiple carriers in a Heterogeneous wireless network (HetNet).
Related Art
Load balance among the multiple carriers in a wireless network is typically a system design goal. Notably, when non-contiguous spectrum with multi-carriers of different bandwidth is involved, different geographical areas may be covered by different numbers of carriers of different bands. The idle redistribution in a system with only macro cell base stations has been studied for years and is well understood. However, Heterogeneous wireless networks (HetNets) introduce many new scenarios, which do not exist in a macro only system and require special treatment. Load balancing may refer to redistribution of idle UEs among available carrier frequencies to avoid overloading of certain carrier frequencies and/or to more efficiently use network resources.
HetNets are deployments of cells with differing coverage radii within a single geographic area. FIG. 1 illustrates an example configuration of a HetNet. As shown, macro cell layer(s) (MC1 and MC2) and small cell layer(s) (SC1-SC6) may have the same or different frequency carriers. There may be multiple small cells of the same or different carriers (carrier frequencies) overlaid with macro cell(s) of the same or different carriers. Overlaid cells may refer to overlap of cells' carrier frequencies. In a conventional macro only system, different carriers may be overlaid with each other such as frequency F1 of MC1 and frequency F2 of MC2, shown in FIG. 1. However, in HetNets, small cell coverage may be only partially overlaid with the macro cell coverage. Different small cells of different carriers may or may not be overlaid with each other (e.g., SC3/SC6 v. SC4/SC5, shown in FIG. 1). Different small cells of the same or different carriers may have different load condition/s. The operator/s of HetNets may also control the load of different carriers/cells based on the Grade of Service (GoS) and Quality of Service (QoS) requirements. As a result, the operator/s may have different load balance requirement/s relative to the macro cell carriers and other small cell carriers. Using the basic idle redistribution method for macro only systems in HetNets may result in a number of problems as described in the following.
First, there may be Ping-Pong problems if there are multiple small cells of the same carrier overlaid with a different macro carrier and the load balance needs of the small cells cannot be differentiated. For example, in FIG. 1, SC1, SC2 and SC4 have the same carrier frequency, F3. Assume SC2 is overloaded, SC1 and SC4 are under loaded (e.g., when SC2 may be a hot spot of activity and SC1 and SC4 are not). The macro layer, e.g. (F1, MC1) may treat SC1, SC2 and SC4 the same as they (SC1, SC2 and SC4) have the same carrier frequency, F3. Therefore, the instruction from the MC1 may only be offloading from F1 to F3 as the conventional macro to small layer offload operation. As a result, idle UEs offloaded from overloaded (F3, SC2) to (F1, MC1) will be ping-ponging between SC2 and MC1 before these idle UEs move out the SC2 coverage.
Second, with a basic probability based solution, the situation of not-enough offload to small cells may occur if multiple small cells of different carriers are overlaid with the macro layer but are not overlaid with each other. For example with respect to FIG. 1, the macro only redistribution method assumes the carriers F1, F2, F3 and F4 are fully overlapped. Therefore, even when the operator intends to instruct 100% of UEs to be redistributed from the macro cell carrier frequencies F1 and F2 to F3 and F4 by setting 50% to F3 and 50% to F4 with 0% to F1 and 0% to F2, at the (F3, SC2) coverage, only 50% of idle UEs reselect to F3 with the 50% to be redistributed to F4, staying with the macro layer (e.g., MC1). This may be due to the fact that at the coverage of (F3, SC2) there is no F4. Therefore, 50% of UEs which have designated F4 with the highest priority to switch to, stay with current serving carrier which is still has higher priority than other carriers until these UEs move into F4 coverage area. Similarly, only 50% of the UEs go to F4 under the SC4 coverage.
Third, when small cells of different frequencies are overlapped, idle UEs should be properly distributed across the overlaid small cells while at the same time preventing Ping-Pongs between the small layers and macro layer as well as among the small cells. For example in FIG. 1, if both SC4 and SC5 are overloaded, the situations of UEs offloading from SC4 to the macro layer and moving to SC5 and vice versa, should preferably be avoided.
Overall, in HetNets additional efforts should be made to address one or more of the new issues introduced by new HetNet scenarios. In HetNets, normally an operator will configure the system to make UEs more likely or have high priority to reselect to the overlaid small cells such that the macro cell layer can offload traffic to the small cell layer.